1,1,2-Trichloro-1,2,2-trifluoroethane (known in the trade under the designation F113) is widely employed in industry for cleaning and degreasing solid surfaces. In addition to its application in electronics to the cleaning of solder fluxes for removing the pickling flux which adheres to the printed circuits, it is possible to mention its applications to the degreasing of heavy metal components and to the cleaning of high quality and high precision mechanical components such as, for example, gyroscopes and military or aerospace hardware. In its diverse applications F113 is in most cases used in combination with other organic solvents (for example methanol), preferably in the form of azeotropic or pseudoazeotropic mixtures which do not demix and which, employed at reflux, have substantially the same composition in the vapor phase as in the liquid phase.
However, F113 forms part of the completely halogenated chlorofluorocarbons which are at present suspected of attacking or degrading stratospheric ozone.
To contribute to solving this problem, the present invention proposes to replace F113-based compositions with a new composition based on 1,1,1,3,3-pentafluorobutane, methanol and 1,1-dichloro-1-fluoroethane. This latter compound, known in the trade under the designation F141b, is practically devoid of any destructive effect on ozone. The same applies to 1,1,1,3,3-pentafluorobutane, known in the trade under the designation F365 mfc.
The composition to be employed according to the invention contains from 60 to 90% by weight of F141b, from 9 to 33% of F365 mfc and from 1 to 7% of methanol. In this range there is an azeotrope whose boiling point is 29.1.degree. C. at normal atmospheric pressure (1.013 bar) and the composition according to the invention has a pseudoazeotropic behaviour, that is to say that the composition of the vapour and liquid phases is substantially the same, which is particularly advantageous for the intended applications. The F141b content is preferably chosen between 75 and 82% by weight, that of F365 mfc between 15 and 21% by weight and that of methanol between 3 and 4% by weight.
The composition according to the invention additionally has the major advantage of not exhibiting any flash point under the standard conditions of determination (ASTM standard D 3828); the composition is therefore nonflammable.
The F141b/F365 mfc/methanol azeotrope is a positive azeotrope since its boiling point (29.1.degree. C.) is lower than that of the constituents (F141b: 32.degree. C.; F365 mfc: 40.degree. C.; methanol: 65.degree. C.).
As in the known compositions based on F113, the composition according to the invention can be advantageously stabilized against hydrolysis and/or radical attacks likely to arise in the cleaning processes, by adding to it a conventional stabilizer such as, for example, a nitroalkane, it being possible for the proportion of stabilizer to range from 0.01 to 5% relative to the total weight: F141b+F365 mfc+methanol.
The composition according to the invention can be employed in the same applications and using the same techniques as the previous compositions based on F113.